Dynamic range control and equalization of digital audio using warped processing

Abstract

This invention describes a method for adjusting the loudness and the spectral content of digital audio signals in a real-time using warped spectral filtering. A warped processing module modifies a spectral content of a digital audio signal with a set of gains for a plurality of non-linearly-scaled frequency bands determined by a warping factor λ of a warped delay line. Warped delay line signals, generated by the warped delay line, are processed by a warped filter block containing multiple warped finite impulse response filters, e.g., Mth band filters, using individual warped spectral filtering in said plurality of the non-linearly-scaled frequency bands, which is followed by a conventional processing by a dynamic range control/equalization block. The present invention describes another innovation, that is embedding the warped processing module in a two-channel quadrature mirror filter (QMF) bank for improving processing efficiency at high sample rates.

Description

FIELD OF THE INVENTION [0001] This invention generally relates to acoustic signal processing and more specifically to adjusting a loudness and a spectral content of digital audio signals in a real-time using warped spectral filtering. BACKGROUND OF THE INVENTION [0002] 1. Field of Technology and Background [0003] A time-varying modification of a loudness is commonly referred to as a dynamic range control (DRC), and it is typically used to amplify quiet audio signals so that they become clearly audible. A static modification of a spectral content is commonly referred to as an equalization (EQ), and it is typically used to amplify some parts of the spectrum according to user preferences, or in order to compensate for a non-ideal response of a transducer such as a loudspeaker. Consequently, the DRC can be used to maximize the loudness of a music track or a ringing-tone whereas the EQ can be used to implement a ‘bass-boost’. [0004] 2. Problem Formulation [0005] When a digital audio sour...

AI Technical Summary

Benefits of technology

[0038] The present invention is computationally very efficient in terms of both required memory resources and a number of MIPS (millions instructions per seconds). The key component is the WFIR filter bank suitable for logarithmically spaced center frequencies. At high sample rates a 2-band QMF bank is used to reduce the processing load, both in terms of the MIPS and the memory resources, by approximately 40%. The WFIR filter bank uses a carefully selected set of Mth band filters that provide an excellent match to the target magnitude response defined by a set of gains. The group delay funct

Problems solved by technology

Cascading is the most natural choice since the resulting magnitude response is easy to predict (it is the product of the individual magnitude responses) whereas adding can cause unpredictable interference unless the phase response of the individual filters are the same.

The main problem with the methods mention

Images